Cargo restraints prevent cargo containing unit load devices (ULDs) such as pallets and containers from moving during transport. This ensures that the goods that are contained in the ULDs arrive at their intended destinations undamaged. Also, by preventing the movement of the ULDs during transport, the restraints ensure that the ULDs do not contact and thereby cause damage to the hull of the transport vehicle.
Typical cargo restraints are stationary and provide no biasing or movement. This is because the restraints must endure the high loads and forces exerted by the ULDs being restrained. Accordingly, most restraints of the prior art are designed as fixed structures offering no flex when configured to restrain a ULD.
Cargo restraints are set in position relative to the cargo compartment of the transport vehicle. The position of the cargo restraints in the cargo compartment is set by coupling the cargo restraints to one or more tracks that line the deck of the cargo compartment. Various standardized tracks, such as a “seat track”, may be used to set the position of the cargo restraints within the cargo compartment of the transport vehicle. The tracks allow the positions of the cargo restraints to be set to accommodate ULDs of different sizes and dimensions. The cargo restraints can be repositioned by manually uncoupling the restraints from the track and recoupling the restraints to a different position on the track.
FIG. 1 illustrates a common configuration for a cargo compartment of an airplane from a top view. As shown, the deck 110 of the cargo compartment is lined with rollers 120 and tracks 130 and 140.
The rollers 120 include lateral oriented rollers and longitudinal oriented rollers. Alternatively, the rollers 120 may include swiveling rollers that can be oriented either laterally or longitudinally as needed. The rollers 120 can be positioned in between the tracks or are attachments that are coupled to the tracks. The rollers 120 eliminate much of the friction between the bottom of the ULDs and the deck 110 of the cargo compartment, thereby allowing ULDs to be repositioned with less force.
One or more centerline tracks 130 are located towards the center of the cargo compartment. One or more side tracks 140 are located towards either sidewall of the cargo compartment. Each track includes alternating open and closed fittings (e.g., open fitting 170 and closed fitting 175). The open fittings are sized to accept studs or other mounting hardware of the restraints 150. The studs are inserted into the open fittings at desired locations along the tracks 130 and 140. The positions of the restraints 150 are then secured by sliding the restraints 150 such that the studs are aligned with the closed fittings instead of the open fittings. Each cargo restraint 150 contains a flange that engages a ULD 160 to prevent the ULD 160 from movement during transport.
Typical cargo restraints are deficient in aircraft transport because of the cargo compartment distortion phenomenon that occurs primarily within the wing box of the airplane. The distortion results from the flexion of the airplane's wings during flight or other movement (e.g., taxiing down a runway). As shown at 210 in FIG. 2, upward flexion of the airplane's wings causes concave distortion 215 to the deck of the cargo compartment on which the ULDs are loaded. As shown at 220 in FIG. 2, downward flexion of the airplane's wings causes convex distortion 225 to the deck of the cargo compartment on which the ULDs are loaded. The amount of distortion varies on hull design, structural materials, and outside forces such as turbulence which can exert greater forces on the wings to produce greater flexion and distortion.
The distortion alters the width of the cargo compartment deck. This distortion when coupled with fixed or stationary cargo restraints of the prior art can result in damage to the aircraft, ULDs, or goods contained within the ULDs. For example, when the distortion creates an expansion of the cargo compartment deck, the restraints may disengage from the ULDs, thereby allowing the ULDs and their contained goods to shift during transit. Alternatively, when the distortion creates a pinching of the cargo compartment deck, the loads of the ULDs become disproportionately distributed to the center of the cargo compartment deck. This can overload the center of the cargo compartment and cause fracturing or other damage to the cargo compartment deck. Distortion of the cargo compartment deck can also cause the cargo restraints to exert penetrating forces to the outer walls of the ULDs. Sufficient penetrating forces can damage the ULDs by breaching or bending the outer walls of the ULDs, thus impacting and damaging the goods contained therein.
Some attempts have been made to engineer attenuating cargo restraints to overcome the deficiencies of fixed or stationary cargo restraints. The attenuating cargo restraint is one such attempt. The attenuating cargo restraint remains stationary relative to the ULD being restrained, but moves relative to itself in order to mitigate the effects of the distortion to the deck of the cargo compartment to which the restraint is coupled. U.S. Pat. No. 7,988,391 describes one such attenuating cargo restraint. While overcoming some of the distortion effects, the described attenuating cargo restraint of U.S. Pat. No. 7,988,391 is limited in practical usage because of various design inefficiencies. Primarily, the described attenuating cargo restraint houses the elastic element (e.g., spring, coil, leaf-spring, etc.) behind the head assembly that engages a ULD. This design inefficiency necessitates an elongated base or frame that extends outboard from where the head assembly engages the ULD. Consequently, the attenuating cargo restraint requires a large distance buffer or clearance between where the restraint engages a ULD and where the restraint is coupled to a track. This design inefficiency prevents the attenuating cargo restraint from being mounted within the plan-view envelope of the cargo being restrained. This design inefficiency further prevents the restraint from use in various aircraft that have constrained outboard specifications or limited spacing between coupling location and an outer sidewall of the cargo compartment. Even when such an attenuating cargo restraint is usable, the outboard extension of the restraint results in lost space in the cargo compartment and thus, suboptimal usage of the available cargo capacity of the transport aircraft. Stated differently, payloads restrained by such an attenuating cargo restraint must be reduced or shrunk laterally in order to recover the width in the cargo compartment that is lost as a result of the outboard extension of the attenuating cargo restraint that extends beyond the head assembly engaging the ULD.
Accordingly, there is a need for a more compact and space efficient attenuating cargo restraint. Such an attenuating cargo restraint is needed to overcome the distortion effects occurring within the cargo compartment of aircraft without sacrificing payload capacity of the aircraft. In other words, the payload capacity of the aircraft cargo compartment and the size of the ULDs transported therein should not be compromised in order to accommodate the attenuating cargo restraint and the attenuating cargo restraint should mount completely within the plan-view envelope of the ULD being restrained.